Role Of P429R,a Point Mutation Of DGCR2 Related To Schizophrenia

The 22q11.2 deletion syndrome(22q11DS)is a neurogenetic condition caused by a microdeletion in chromosome 22 with a high risk for developing schizophrenia(SCZ).About 23~43% of 22q11 DS patients develops SCZ.DGCR2(DiGeorge syndrome critical region gene 2)is one of the deleted genes among critical region within 22q11.2 deletion and itself is also associated with SCZ.Reduced expression of DGCR2 has been found in SCZ patients.Recently,an exome sequencing study found a de novo missense mutation(P429R)in DGCR2 is associated with SCZ.However,it is largely unclear that how P429 R mutation impairs DGCR2 functions and participates in SCZ pathogenesis.We used site-directed mutagenesis PCR to construct DGCR2-P429 R mutant mammalian expression vector and transfected it into the cell line.P429 R expression level is comparable to wild type(WT)of DGCR2,but it migrates faster than WT on SDS-PAGE.The relative molecular weight of P429 R is 8kDa(kilo-Dalton)smaller than that of WT.Furthermore,P429 R was overexpressed in primary cultured hippocampal neurons and found that its distribution in the neurons is similar to WT.DGCR2 is a single transmembrane protein that is mainly localized to the postsynaptic densities(PSDs).DGCR2 can interacts with PSD-95,a scaffolding protein in PSDs,through its PDZ-binding motif within the intracellular domain(ICD)of DGCR2.The P429 R mutation doesn't alter its interaction with PSD-95.SCZ is a neurodevelopmental disorder,and we found that the expression of DGCR2 is increased during the critical period for dendrite and synapse development.So we used shRNAs(short hairpin RNAs)to knockdown DGCR2 expression in primary cultured hippocampal neurons during this period.The length and complexity of dendrites,as well as dendritic spine density are decreased upon DGCR2 knockdown.However,these deficits can be rescued by overexpressing WT of DGCR2,but not P429 R.These results suggest DGCR2 regulates dendrite and dendritic spine development,and P429 R mutation may impair the functions of DGCR2 on neurodevelopment,and lead to SCZ.Our findings will be helpful for further understanding the molecular physiopathological mechanisms of DGCR2 in SCZ.